At the start screen, press leftshift and click with the mouse on the round loudspeaker. You then have access to the Giant Ant mission! If you are playing this mission, try to protect you vehicles and buildings to the best of your ability. Build as many Infantry units as you can, because they are the most effective against the ants. Be sure you have a couple of medics handy too.
Extra Tanks
While the game is loading, type XPEINA518 and you should get 30 extra medium tanks at the beginning of the battle. Be sure to enter the code in all caps.
Helpful Shooting
Always tap the fire key when shooting as this will keep the gun more accurate.